Neptune`s Blue Moon Inspires Wonder In Scientific Circles

August 24, 1989|By Ronald Kotulak, Chicago Tribune.

PASADENA, CALIF. — Neptune`s natural satellite Triton, which has been called one of the most unusual objects in the solar system, lived up to its advance billing Wednesday as images from Voyager 2 revealed that it is a partly blue moon.

As the spacecraft approaches Neptune for its close encounter Thursday night, its cameras are revealing a kaleidoscope of colors on Triton that range from red to blue, with a touch of pink and white.

``If it is indeed blue, it is the only blue thing we`ve seen on any satellite since we launched Voyager,`` said Bradford Smith, the University of Arizona astronomer who heads the Voyager imaging team at the Jet Propulsion Laboratory in Pasadena.

Images of Triton show a large blue zone in the area where sunlight changes to darkness on the moon. It is in this area that a movable frost of methane and nitrogen appears to be condensing.

Voyager, which was launched 12 years ago on a grand tour of the giant outer planets, has already revealed spectacular sights including a volcanic moon around Jupiter, Saturn`s bright rings and Uranus` ice-sculpted satellites.

But Triton, the only moon to orbit a planet in the opposite direction of the planet`s rotation, may top the earlier celestial shows.

A visitor from Earth might feel a little at home on Triton, where he could look toward the horizon and possibly see a blue sky, said Smith. But he might be a bit unnerved at the blue ground beneath his feet in some areas.

Triton`s blue sky and ground may be caused by tiny ice crystals of methane and nitrogen that make up the moon`s atmosphere, said Smith.

The Earth`s blue sky is caused by gas molecules in the atmosphere that scatter light from the Sun that is of shorter wavelengths than in the blue spectrum. The tiny molecules of frozen methane and nitrogen in Triton`s atmosphrere may be scattering light in the same blue spectrum, said Smith.

Triton, which is about the same size as Earth`s Moon, will get a close-up look from Voyager Friday when the spacecraft zooms within 25,000 miles of it. Voyager continues to amaze scientists with images of Neptune.

``We`re all excited because the images just keep getting better and better,`` said Smith. ``We have people literally jumping up and down.``

The excitement is being generated by the discovery of unexpected activity in Neptune`s atmosphere. Some high, cirrus-like clouds appear and disappear faster than scientists can track them.

A cloud formation called ``Scooter`` circles Neptune every 16 hours, the same time the planet takes to make a revolution on its axis, and scientists are so puzzled by this phenomenon that they have devised no explanation for it.

Features at different latitudes travel at vastly different speeds. A small dark spot, which is a hurricane-like storm system near the planet`s south pole, laps a great dark spot at a higher latitude every five days. The great dark spot, another storm system, is the size of Earth.

``The features in Neptune`s atmosphere change a lot faster than we ever expected them to,`` said Smith.

At a distance of about 2 million miles, instruments aboard Voyager detected the first radio emissions from Neptune, indicating that the planet may have a magenetic field that is slightly stronger than Earth`s, said Edward Stone, a California Insitute of Technology physicist who is Voyager project scientist.